Poets don't know any more to whom their letters are addressed. Any poet writing a letter now may also be writing it for the reader of his selected letters, who will be reading it for all sorts of reasons. If once we read, say, Keats's letters to get closer to the source, to find out what the writer was really like - 'really like' meaning off the record, in private - now we have to read them to find out what the writer was really like when he was writing letters that may be published ('If it ever strikes you that my letters are cool or cramped, now you know why,' Hughes writes to his lover Assia Wevill and, indeed, we do know why).

So the pressures on the modern letter-writing poet are complicated. After reading Keats's letters or, indeed, Cowper's or Yeats's or Lowell's, the poet will want to compose letters that really say something and that add to the work. After reading Larkin's letters, with their sniggering racism and misogyny, the poet will be rather more cautious about saying what he happens to think ('All that self-loathing, at full spurt, bubble, ooze and drip,' as Hughes remarks after reading Larkin's letters). Given what people knew or, rather, thought they knew about Ted Hughes in his lifetime, most notoriously the suicides of his wife Sylvia Plath and his lover Wevill, one might have imagined that in his private correspondence, he would have been under considerable pressure; pressure not to give too much away and pressure to be able to give way; to say everything that couldn't and shouldn't be said.

'My life,' he writes in a late letter, 'would have been ruined by what other people have said about what they thought I said, or did, on occasions - if I had let it be.' These remarkable letters, surely among the best poet's letters that have been published, are a testament to his powers of resistance and to his shrewd and unselfserving intelligence, which is often startling in its insights and intuitions and, indeed, in its lack of defensiveness.

Hughes is one of the very few writers who can write about privacy without making you think he is hiding something. Everything he touches on in these letters - marriage, family life, ecology, writing, fishing, Shakespeare, mink farming, America, the condition of England, academics, astrology, the royal family, religion, suicide, education - is released from cliche and dull prejudice. Like his poems, the letters seek a stripped-down clarity, whatever their subject, not sophisticated revelations or clever attitudes. So these letters are not merely commentary and comment and opinion, they are poetry by other means.

An acutely self-conscious poet, most of whose poetry is acutely about selfconsciousness - it was the obscure, furtive single-mindedness of the natural world that Hughes wrote about - his war against self-exposure is continued in his letters. For Hughes, self-promotion was the enemy of poetry, the very thing, quite literally, that spoiled writing (and the very thing that made him, then as now, not even a fashionably unfashionable writer). 'My definition of "poetry",' he writes, with characteristic generosity, to a student who had sent him a few questions, 'almost excludes anything coming from the ego under the ego's control... my whole writing career sometimes presents itself to me as a search for not one style in particular, but the style for this crisis or that.' The poet is not in search of a 'voice', or a position, or indeed a career; he is in search of a survival kit, of words that because they get him through get through to other people.

So the letters sometimes make plain what the poetry performs. 'Almost all art,' Hughes writes to American artist Leonard Baskin , 'is an attempt by someone unusually badly hit (but almost everybody is badly hit), who is also unusually illequipped to defend themselves internally against the wound, to improvise some sort of modus vivendi... in other words, all art is trying to become an anaesthetic and at the same time a healing session.' The artist is the person who because he is so much in need of anaesthetics - and is therefore tempted to trade in them - must also, 'at the same time' be able to resist them. The risk, for Hughes, is that art puts us to sleep just when we need to wake up.

In Hughes's view, the problem of what he calls, in a letter to poet and translator Daniel Weissbort , 'the whole modern movement in poetry and the attitudes of technologists and scientists' is that everyone involved is 'incapable of making a statement that doesn't seem in a real human situation, supercilious, bookish, inadequate, frivolous, irrelevant etc'. Again and again in these letters, Hughes reports on what he thinks of as at once a cultural malaise (of Britain after the wars: 'after the First World War [in which his father fought] the whole country was traumatised... I passed my early days in a kind of mental hospital of the survivors, widowers etc') and a personal crisis, the deaths of two much-loved women and a child. And the crisis for Hughes has to do with living in the aftermath of these catastrophes that can neither be faced nor impressively ignored, and that are in some way linked in his mind.

Because Hughes is never histrionic, the really gruelling anguish he felt about Plath's suicide is everywhere in these letters, but everywhere understated. It was what he called, in writing about Shakespeare, 'the crowded, howling universal concept of catastrophe' that obsessed Hughes. He was fortunate enough to believe that there was something that could still be recovered - that what he calls in a letter to a student the 'mentally sick' could be cured by being 'put in contact with their real nature'. There was a real nature, he believed, and it had been viciously attacked and suppressed in the 17th century by the puritans and virtually eradicated by the two world wars. His poetry was about what if anything was left of this real nature; and his inspired and cranky (and often convincing) book on Shakespeare, Shakespeare and the Goddess of Complete Being (1991 ), was the fashioning of an explanatory myth of the decline and fall of British culture.

His letters inevitably elaborate these preoccupations with a great deal of plain eloquence and idiosyncratic erudition and, it should be said, without grandiosity or portentousness. Because Hughes is radically preoccupied, there is a strange, unboastful modesty in these letters. Even in his prejudices - against Auden, against literary London, against many of his contemporary poets - he is never supercilious. Indeed, Hughes's tone as a writer is one of the most original things about him.

But the guiding thread from the beginning to the end of his extraordinary project is the idea of poetry as shamanistic, of the poet as healer rather than seducer or charmer, or comforter or entertainer. Poetry, he writes to an interested bishop, is 'nothing more than a facility... for expressing that complicated process in which we locate, and attempt to heal, affliction... the physical body, so to speak, of poetry is the treatment by which the poet tries to reconcile that pain with the world'. There is a potentially daunting earnestness, or even quaintness, in this; later in the same letter, Hughes adds: 'I regard poets such as myself as a sort of country healer', but these letters, rather like the poems, are so averse to cuteness and complacency that the writing and the writer always seem more interesting than the views expressed.

Hughes is unfathomably and inexhaustibly interesting, especially when writing about what reading and writing have to do with growing up and getting by (this book is worth buying for his letters to his children alone). So however eccentric Hughes sometimes sounds in these letters - and the insistent astrology, not to mention the mink-farming project, are not, as Hughes knows, everyone's cup of tea - the reader never loses confidence in Hughes's distinctive voice (and confidence). Because he has such a sure sense of what interests him, and that what interests him matters to him, the reader of these letters always feels addressed. Hughes has the knack, which is something to do with the intimate impersonality of his writing, of speaking to someone in particular, and to anyone else at the same time. So the letters, most of which are straightforwardly heartfelt whatever the matter at hand, never leave you feeling that you are eavesdropping.

Larkin's now infamous letters didn't merely expose him as not as nice as we wanted him to be; they also exposed just how narrow-minded and wishful our assumptions about poets (and character) are. These remarkable letters, so carefully and cannily edited by Christopher Reid are not an exposé of anything, or anyone. Hughes was the least cagey of writers, and the least confessional. (Confession is only for people who already know what's wrong with them, and knowingness was Hughes's bete noire.) These letters simply confirm that everything he wrote is worth reading; and partly because of something he ascribed to Shakespeare, 'his near pathological attitude to falsity, and his corresponding truth to himself'.